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  1. ESPcomposites

    Single shear joint fastener flexibility comparison to FEM

    Oh, I forgot, 1D Elements can handle this problem as well ( https://www.structuralfea.com/1D_Elements/1D_Elements.html ). It uses MYSTRAN and I attached an example. Brian www.espcomposites.com
  2. ESPcomposites

    Single shear joint fastener flexibility comparison to FEM

    You can try out eDistribution as well (https://www.espcomposites.com/software/download.html). There is an input for a manual fastener flexibility. Brian www.espcomposites.com
  3. ESPcomposites

    Know of Shell Element Formulations with Differential Stiffness Matrix?

    Does anyone of know shell element formulations (tri and quad) that have an associated differential stiffness matrix (geometric stiffness matrix)? The MITC elements are quite popular, but we can not find the associated differential stiffness matrix. The objective is to incorporate these...
  4. ESPcomposites

    Bearing-Bypass Interaction Basics

    I am not sure that is a good analogy. A bearing-bypass curve is an interaction curve, but it takes multiple test data points to fit it. Also, the curve itself it a function of various factors (so it takes quite a bit of empirical data to generate a set of curves that could be used for practical...
  5. ESPcomposites

    Why are open source FEA tools so far behind commercial FEA tools?

    Some potential users: - Students who don't want to use limited codes - Small companies (general) - Small/large companies that want unlimited number of licenses for large runs - (Similar to above) Small/large companies that want to use FEM in combination with in-house tools (hybrid solutions)...
  6. ESPcomposites

    Why are open source FEA tools so far behind commercial FEA tools?

    You might want to have a look at www.mystran.com. MYSTRAN is similar to NASTRAN (the decks are almost equivalent), but has a modern code base (the NASTRAN source is very old and quite difficult to work with). We are doing to some great things with it. It will be incorporated into FreeCAD at some...
  7. ESPcomposites

    Nonlinear buckling occurs earlier than linear buckling?

    Are you familiar with a beam-column analysis? If not, look it up. In essence, the the magnitude of the moment in the beam-column is analogous to an increasing imperfection. Brian www.espcomposites.com
  8. ESPcomposites

    Nonlinear buckling occurs earlier than linear buckling?

    Linear buckling represents the theoretical maximum capability (representative of the slightest imperfection). Any imperfection that is greater than "the slightest" (i.e. a typical nonlinear analysis) will result in a lower buckling load (at least for the initial bifurcation - which is not always...
  9. ESPcomposites

    Euler and Global/Local Buckling

    On the structural analysis side, we would consider global buckling of a column to be the "overall buckling" of the cross section. The entire column curves in this scenario (but the deformed cross section has the same shape throughout the column - at least at the macroscopic level). If we...
  10. ESPcomposites

    Different Buckling load Factors for Same Model, Different Software

    Have all 3 solutions converged though? There will be discrepancies when the model is not converged, but I would expect those them to decrease once the model has reached convergence. Brian www.espcomposites.com
  11. ESPcomposites

    Is there any freeware solver to solve plate buckling?

    https://www.structuralfea.com/PlateMesh/PlateMesh.html Brian www.espcomposites.com
  12. ESPcomposites

    Which constraints should I set to simulate stiffened panel under pure shear?

    You can have a look here under the INDIVIDUAL DOCUMENTS section. For the Basic Manual, Page 7 discusses the boundary conditions and some specifics about it. The Validation Cases PDF shows that this approach is accurate for in-plane loading (Nxy loading)...
  13. ESPcomposites

    Plate Deflection: FEM vs. hand calculation

    Items to consider for nonlinear geometry 1. For a linear analysis, the assumption is sin(theta)=theta (small deformation assumption). However, as this assumption changes, so can the result. This will also depend if the force is a "follower force" or not (meaning the angle of the force changes...
  14. ESPcomposites

    Connection Design in Finite Element Analysis

    Megastructrues, No, that is not what I am saying. I think I confused you, so I will try to keep it simple. Simply input the load-deflection of the connection to the FEA (whether it is linear or nonlinear, depending on your goals)...that is all. The load-deflection curve may look something like...
  15. ESPcomposites

    Connection Design in Finite Element Analysis

    Here is a basic overview. There are some details I left out, but this is the basic concept. 1. Start with testing a single joint connection (a single fastener and its plate members). It could be singe shear, double shear, etc. Apply a load to the plate and recover the total deflection. Next, we...
  16. ESPcomposites

    Connection Design in Finite Element Analysis

    The load-deflection curve is just another way to determine the "connection stiffness" or "fastener flexibility". Its nothing more than F=kx. The reason I chose to say load-deflection is that it implies consideration for the nonlinear range (since load and deflection are the direct outputs from...
  17. ESPcomposites

    Connection Design in Finite Element Analysis

    Perhaps this may help? Your first start with determining the load-deflection curve (linear or nonlinear) of the individual connection. This could from a semi-empirical equation or directly form test data. You then use the FEA to represent the actual structure (may have many fasteners), where a...
  18. ESPcomposites

    Connection Design in Finite Element Analysis

    Human909: You may be correct about the argument being made. So perhaps the question is what is the usefulness of a linear vs nonlinear model, even if just a spring is used to represent the connection (as opposed to using a FEA itself to determine the load-deflection response of the connection)...
  19. ESPcomposites

    Connection Design in Finite Element Analysis

    Sounds good. Make sure to be familiar with the various deformation/failure modes and try to understand what would be required to model that in FEA. Note that you could probably determine the linear connection stiffness via FEA (provided it is a 3D model with contact). But with a lot of effort...
  20. ESPcomposites

    Connection Design in Finite Element Analysis

    Well, for the linear range, there are semi-empirical solutions for the effective "fastener flexibility" (the compliance of the joint connection), which are based off of test. Assuming the connection is bearing critical and large deformation is expected, you could develop an approximate nonlinear...

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